Matrix dimensions must agree.

Where is problem? please helpp me ;(((

function ptcd_ptqd
clc
clear var1
clear var2
close all

%% NHAP DU LIEU
t = linspace(0,5,6);

%% TINH TOAN TOA DO
x = 3*t.^2-(4/3*t.^3) ; % hoanh do [m]
y = 8*t ; % tung do [m]

dt = diff(t);
dx = diff(x);
dy = diff(y);
%% TINH TOAN VAN TOC
vx = dx./dt ; % thanh phan van toc theo phuong ngang [m/s]
vy = dy./dt ; % thanh phan van toc theo phuong thang dung [m/s]
v = sqrt(vx.^2+vy.^2); % van toc

dt = diff(t);
dvx = diff(vx);
dvy = diff(vy);
%% TINH TOAN GIA TOC 
ax = dvx./dt;  % thanh phan gia toc theo phuong ngang [m/s^2]
ay = dvy./dt ; % thanh phan gia toc theo phuong thang dung [m/s^2]
a = sqrt(ax.^2+ay.^2); % gia toc

%% FIGURE
figure('name','Toa do','color','white','numbertitle','off');
plot(t,x,'linewidth',2);
xlabel('Thoi gian');
ylabel('Toa do [m]');

figure('name','Van toc','color','white','numbertitle','off');
plot(tv,v,'linewidth',2);
xlabel('Thoi gian');
ylabel('Van toc [m/s]');

figure('name','Gia toc','color','white','numbertitle','off');
plot(ta,a,'linewidth',2);
xlabel('Thoi gian');
ylabel('Gia toc [m/s^2]');

end

Answer 1

[Image Analyst]

dt does not have one element for every element. It has one element for every PAIR of elements. Since all your dt are the same, just do this

dt = t(2) - t(1);

to get the difference between any two t elements (since the spacing is uniform).